Photoactivity of green microalgae is nonmonotonic across the electromagnetic spectrum. Experiments on Chlamydomonas reinhardtii (green alga) and Cyanothece 51142 (green-blue alga) show that wavelength specific backscattering in the blue region of the spectrum from Ag nanoparticles, caused by localized surface plasmon resonance, can promote algal growth by more than 30%. The wavelength and light flux of the backscattered field can be controlled by varying the geometric features and/or concentration of the nanoparticles.

Multicomponent plasmonic nanogels (PNGs) capable of broadband absorption of light in the 400−700 nm wavelength range were synthesized by the self-assembly of metal nanoparticles with wormlike surfactant micelles. Small angle x-ray scattering and rheological experiments suggest that the nanoparticles bridge micelle fragments to aid the formation a stable gel phase with exceptional color uniformity. Their optical absorbance could be robustly tuned by changing the nanoparticle type (Au/Ag), size, shape, and/or concentration. The PNGs have relatively low viscosity and are thermoreversible. Potential applications to the manufacturing of coatings and interfaces for solar energy harvesting and reconfigurable optical devices can be envisioned.

An effective-medium theory (EMT) is developed to predict the effective permittivity ε eff of dense random dispersions of high optical-conductivity metals such as Ag, Au, and Cu. Dependence of ε eff on the volume fraction ϕ, a microstructure parameter κ related to the static structure factor and particle radius a, is studied. In the electrostatic limit, the upper and lower bounds of κ correspond to Maxwell-Garnett and Bruggeman EMTs, respectively. Finite size effects are significant when jβ 2 ka∕n 3 j becomes O1, where β, k, and n denote the nanoparticle polarizability, wavenumber, and matrix refractive index, respectively. The coupling between the particle and effective medium results in a red-shift in the resonance peak, a nonlinear dependence of ε eff on ϕ, and Fano resonance in ε eff .

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Low viscosity fluids with tunable optical properties can be processed to manufacture thin film and interfaces for molecular detection, light trapping in photovoltaics and reconfigurable optofluidic devices. In this work, self-assembly in wormlike micelle solutions is used to uniformly distribute various metallic nanoparticles to produce stable suspensions with localized, multiple wavelength or broad-band optical properties. Their spectral response can be robustly modified by varying the species, concentration, size and/or shape of the nanoparticles. Structure, rheology and optical properties of these plasmonic nanogels as well as their potential applications to efficient photovoltaics design are discussed.